1. Field of the Invention
The present invention relates generally to a lens barrel attachable to and detachable from a main body of an optical apparatus such as a video camera, a still camera and a monitor camera, and more particularly to a lens barrel incorporating a lens system a closest-to-main-body lens of which is moved, and also a lens barrel including, e.g., an inner focus type zoom lens.
2. Related Background Art
In recent years, a typical zoom lens as a conventional art zoom lens used for this kind of optical apparatus has been of a so-called inner focus type or rear focus type constructed such that focusing is performed by use of a lens unit located more rearward than a varieter lens instead of a theretofore prevailing so-called front lens element focus system wherein the foremost lens unit serves as a focus lens. With this inner focus lens arrangement, phototaking at the closest focusing distance becomes more possible than by a front focus lens arrangement, and the arrangement may be easily constructed to perform continuous focusing from just anterior to the lens up to the infinity especially on the wide-angle side.
A variety of lens types of the inner focus zoom lens are known. FIG. 1 illustrates a lens constructed of 4 lens units, wherein the rearmost lens unit is employed for focusing. Referring to FIG. 1, there are shown a fixed front lens unit 111, a varieter lens unit 112 for changing a focal length, a fixed lens unit 113, and a focus lens unit 114 for focusing and compensating a change of focus position when changing the focal length.
Shown also are a rotation preventive guide bar 133, a feed bar 134 for the varieter lens unit 112, a fixed lens barrel 135, a stop unit 136 (herein inserted at a right angle to the paper sheet surface), a step motor 137 defined as a focusing motor, an output shaft 138 of the step motor 137, whose shaft is worked to form a male thread 138a for moving the lens unit 114. A female threaded portion 139 meshing with the male thread 138a is integral with a moving frame 140 for the lens 114.
Shown further are guide bars 141, 142 for the lens 114, a rear plate 143 for positioning and holding the guide bars 141, 142, a relay holder 144, a zoom motor 145, a decelerator unit 146 of the zoom motor 145, and interlocking gears 147, 148, the gear 148 being fixed to the zoom feed bar 134.
An operation of the lens shown in FIG. 1 will be explained. When driving the step motor 137, the focus lens 114 is moved in the optical axis directions by the help of the screw feed. Further, when the zoom motor 145 is driven, the screw shaft 134 is rotated through the interlocking gears 147, 148, and the varieter lens unit 112 held in the lens frame 112a that meshes with the screw shaft 134 is moved in the optical axis directions.
FIG. 2 is a graph showing a positional relationship of the varieter lens unit 112 versus the focus lens unit 114 in the lens barrel constructed as shown in FIG. 2, corresponding to some object distances. FIG. 2 shows more specifically the focusing positional relationship with respect to respective objects located at an infinite distance, 2 m, 1 m, 80 cm and 0 cm. As shown in FIG. 2, in the case of the inner focus, the positional relationship between the varieter lens unit 112 and the focus lens unit 114 differs depending on the object distance, and hence the focus lens unit 114 cannot be interlocked by a mechanical structure as in the case of a cam ring of the front focus lens.
Then, it is indispensable to control the positions of the respective lens units 112, 114 in accordance with the object distance so as to satisfy the positional relationship between the lens units when zooming as shown in FIG. 2. It is proposed that trajectory tracing methods each showing the positional relationship between the varieter lens unit 112 and the focus lens unit 114 in accordance with the object distance in Japanese Patent Application Laid-Open Nos.1-280709 and 1-321416.
FIG. 3 is a diagram showing a construction of a video camera in which this trajectory tracing method is carried out. The numerals 111 to 114 represent the same lens units as those shown in FIG. 1. A position of the varieter lens unit 112 is detected by a zoom encoder 149. Herein, an encoder type conceivable herein may be a volume encoder constructed so that a brush integrally attached to a varieter moving ring slides on a substrate printed with a resistance pattern.
A stop encoder 150 for detecting a stop value involves the use of an output of a hall element provided in, e.g., a stop meter. The numeral 151 designates an image pick-up element such as a CCD, etc., and the numeral 152 represents a camera processing circuit. Y-signals are taken in an AF circuit 153. This AF circuit 153 determines whether the object is focused or defocused. If defocused, there may be made determinations as to whether anterior or posterior focusing is effected, or what degree the object is defocused to. Results thereof are inputted to a CPU 154.
A power-ON reset circuit 155 performs a variety of reset operations when switching ON the power supply. A zoom operation circuit 156 transfers, when the operator operates a zoom switch 157, a content thereof to the CPU 154. The numerals 158 to 160 designate memories for storing the trajectory data shown in FIG. 2. The memories are the direction data memory 158, the velocity data memory 159 and the boundary data memory 160.
Shown also therein are a zoom motor driver 161 and a step motor driver 162. The CPU 154 continuously counts up the number of input pulses supplied from this step motor driver 162 to the step motor 137, and this count number is used by an encoder for obtaining an absolute position of the focus lens unit 114.
By such a construction, the positions of the varieter lens unit 112 and of the focus lens unit 114 are obtained from the number of input pulses of the step motor 137 as well as by the zoom encoder 149, and therefore one point on a map shown in FIG. 2 is determined from the positions of the above two lens units.
On the other hand, the map shown in FIG. 2 is segmented into small zones I, II, III, ... each assuming a rectangular shape as illustrated in FIG. 4 by boundary data 160. Oblique portions are regions where a pair of lens units are inhibited from being disposed. Thus, once one point on the map is thus determined, it is feasible to determine which small zone that one point belongs to.
In the memories, there are the velocity data and the direction data per zone that indicate a rotating speed and direction of the step motor 137, which are obtained from trajectories passing through the centers of the respective zones. For instance, in the example shown in FIG. 4, an axis of abscissas (a position of the varieter lens unit) is divided into 10 zones. Now, supposing that a velocity of the zoom motor 145 is set to move the varieter lens unit from a telescopic end to a wide-angle end in 10 seconds, a passage time through one zone in the zooming direction is 1 second.
FIG. 5 is an enlarged diagram of the block III in FIG. 4. A trajectory 164 runs through the center of this block III, a trajectory 165 passes leftward downward, and a trajectory 166 runs rightward upward. These trajectories have inclinations that are somewhat different from each other. Herein, the focus lens unit is, if moved at a velocity of x mm/1 sec on the central trajectory 164, capable of tracing on the trajectory with substantially no error.
When the thus obtained velocity is termed a "zone representative velocity", the velocity memory is stored with values thereof for only the number of small zones in accordance with the zones. Further, supposing that this velocity is indicated by the arrow 168, a velocity of the step motor is set by minutely adjusting the representative velocity as shown by the arrows 167, 169, depending on results of the detection by the autofocus adjusting device. Moreover, the rotating direction of the step motor 137 varies corresponding to the zones even in the case of zooming from the same telephoto end to the wide-angle end (from the wide-angle end to the telephoto end), and hence the direction data memory is stored with code data thereof.
As discussed above, the position of the focus lens unit is controlled by driving the step motor 137 during the drive of the zoom motor 145, which involves the use of the step motor velocity obtained by compensating the above zone representative velocity from the result of the detection by the autofocus adjusting device with respect to the zone representative velocity obtained from the varieter lens position and the focus lens position as well. The focus position can be thereby kept also during zooming even in the case of the inner focus lens.
Further, there exists a method by which the velocities indicated by the arrows 167, 169 in addition to the representative arrowed velocity 168 in FIG. 5 are memorized, and three velocities are selected corresponding to the results of detection by the autofocus adjusting device.
Excluding the above-described method of memorizing the velocities, there might be employed a method of calculating a trajectory passing through one point on the map that is determined by present positions of the varieter lens unit 112 and of the focus lens unit 114 and tracing on this trajectory, and a method of memorizing a plurality of trajectories as positions of the focus lens unit 114 that correspond to the positions of several varieter lens units 112.
Disclosed in Japanese Patent Application Laid-Open No. 1-321416 is a method of storing data about position of the focus lens unit 114 versus each of a plurality of positions of varieter lens unit 112 between the wide-angle end and the telescopic end with respect to a plurality of object distances (which corresponds to storing the trajectory data in FIG. 2), then recognizing where positions of the varieter lens unit 112 and of the focus lens unit 114 exist within the map when starting the zooming process, subsequently performing, based on that point, interpolation arithmetic from the, stored data of the closest trajectory at the anterior focus side and from the stored data of the closest trajectory at the posterior focus side at the same focal length, and calculating the positions of the focus lens unit at the respective focal lengths (the positions of the varieter lens unit).
FIG. 6 illustrates a trajectory in the vicinity of the telephoto end when zooming. According to Japanese Patent Application Laid-Open No. 1-321416, there are stored pieces of data rr.sub.1, rr.sub.4, rr.sub.7, rr.sub.9 indicating positions of the focus lens unit 114 versus positions V.sub.n (the telephoto end), V.sub.n-1, V.sub.n-2, V.sub.n-3 of the varieter lens unit 112 along a trajectory I (e.g., an infinite distance focusing trajectory). That is, it follows that the trajectory running through points P.sub.1, P.sub.4, P.sub.7, P.sub.10 in the map is stored as the infinite distance trajectory.
Similarly, pieces of data rr.sub.2, rr.sub.5, rr.sub.8, rr.sub.11 indicating positions of the focus lens unit versus the positions V.sub.n (the telescopic end), V.sub.n-1, V.sub.n-2, V.sub.n-3, are stored in the form of trajectory (e.g., a 10 m focusing trajectory). As a matter of course, these data are actually created over the entire zoom region extending from the telephoto end to the wide-angle end.
Herein, when zoomed from the point (V.sub.n, rr) in the map, points P.sub.A, P.sub.B, P.sub.C are obtained by the interpolation arithmetic based on the stored data of the closest trajactory at the anterior focus side in the same position of the varieter lens unit position from the point P, i.e., data of a trajectory II, and similarly the data closest of the trajactory at the posterior focus side, i.e., data of a trajectory I. The trajectory during zooming is determined by thus obtaining the respective positions of the focus lens unit 114 with respect to the focal lengths V.sub.0 (the wide-angle end), V.sub.1, V.sub.2, . . . . V.sub.n-1, V.sub.n (the telescopic end).
Herein, because of the interpolation arithmetic, a ratio of a distance between the points P.sub.1 and P to a distance between the points P.sub.2 and P is equal to a ratio of a distance between, e.g., the points P.sub.A and P.sub.4 to a distance between the points P.sub.A and P.sub.5.
The memory pertaining to the above velocities or positions is constructed based on optical design values when the manufacturing error is set, as a matter of course, to 0.
Note that the following embodiments of the present invention take such a configuration that the second lens in, as in the above-described example, the 4-lens-unit, i.e., convex/concave/convex/convex, inner focus lens is the varieter lens, and the fourth lens is the focus lens, and in addition thereto, may also be adapted to other configurations (shown in FIGS. 5, 7 and 8 in, e.g., Japanese Patent Application Laid-Open No. 3-27011).
Further, in the example shown in FIG. 1, the actuator for zooming involves the use of the DC motor with the gear head. As in the case of the focus lens unit, however, the step motor may also be used. Also, as the encoder for the varieter lens unit, the volume type encoder is not employed, but there may be adopted an encoder for detecting the absolute position of the lens unit by counting the number of input pulses for the reset fiducial position as in the case of the focus lens unit. There is also a method of using a photo interrupter for the reset fiducial position. Known also are method of employing an ultrasonic motor and a method of using a voice coil type as the actuator for each movable lens unit.
The conventional inner focus lens is constructed as described above, and therefore, when this inner focus lens is used as a so-called interchangeable lens interchangeable with respect to a video camera main body, it might happen that a rearmost (closest to the main body) movable lens unit of the interchangeable lens removed is easily touched (including a case of, e.g., cleaning the lens), or a static pressure weight is applied depending on the way it is treated.
In such a situation, for example, according to the construction for moving the rearmost lens unit by use of the above-mentioned step motor, it is impossible to keep a normal image forming performance because of the lens unit deviating or tilting from a normal on-optical axis position due to the fact that an interlocking mechanism of the screw feeding portion is broken, or that an interlock meshing state is inadequate, or deformation caused with the static pressure weighting of the mechanism which holds the rearmost lens unit. Alternatively, there might be a possibility in which dust or water drops carelessly permeate the interior of the lens barrel sufficient to break the respective mechanisms.